These colorful timbales of rice, spinach, and shrimp can be assembled ahead of time and refrigerated for up to 12 hours or frozen for up to a month.
Place the unwashed rice in a heavy saucepan. Crush the saffron threads between your fingers. Add the saffron and 1 teaspoon salt to 3 cups warm water, and stir to dissolve. Add the water to the rice in the pan and bring to a boil, uncovered, over high heat. Reduce heat to medium-low, cover with a tight-fitting lid, and cook 12 to 15 minutes, or until the water is absorbed and the rice is tender. Remove from heat and fluff rice with a fork. Place the cooked rice in a large bowl. Add chopped shrimp and set aside.
In a small nonstick skillet over medium heat, toss the pine nuts until toasted, about 2 to 3 minutes, and set aside. In a medium skillet over medium heat, melt 3 tablespoons of butter. Add the onion and saute 2 minutes, until translucent. Add the garlic and saute 1 minute. Add the spinach and saute until the onions are golden and most of the liquid has evaporated, about 5 minutes. (Drain excess liquid if necessary.) Add the remaining ¼ teaspoon salt, pepper, and nutmeg. Add the pine nuts to the spinach mixture and set aside.
To assemble: Butter the molds. Divide the saffron-shrimp rice equally among the 8 molds, filling each three-quarters full. Press rice firmly into the mold with the back of a spoon. Repeat this process with the spinach-pine nut mixture. Divide the remaining 3 tablespoons of butter into 8 pieces. Place one piece of butter atop each rice mold. You may cover timbales with foil and freeze at this point. Preheat oven to 375 degrees. Place the rice molds right side up on a baking sheet and bake, uncovered, 12 minutes. Invert on individual dinner plates. Tap the bottom of the mold several times, then carefully lift the mold. Garnish each rice mold with a sprig of parsley and a peeled shrimp.